X-ray Fluorescence Analysis of Lead in Tin Plating Using Theoretical Intensity of Scattered X-rays

Introduction

RoHS regulated elements, such as cadmium and lead, are analyzed by energy dispersive X-ray fluorescence spectrometer (EDX). However, the quantitative values obtained by this method are affected by the thickness when the sample is a thin film, such as plating. Therefore, we measured the film thickness in an attempt to correct the quantitative values. The sample was a tin-plated copper resistor terminal. The calibration curve method was used for lead concentration, and the fundamental parameter (FP) method was used for tin thickness. The measurement of lead yielded a quantitative value of 313.4 ppm, and the measurement of tin obtained a plating thickness of 9.1 µm. A thickness correction factor was calculated from the tin plating thickness, giving a final quantitative value of 272.7 ppm for lead. A measurement was performed using an energy dispersive micro X-ray fluorescence spectrometer (µEDX) that is unaffected by the sample shape. The resulting 269 ppm quantitative value for lead approximately matched the EDX quantitative value. Other samples, such as a display terminal, diode terminal, and washer, were also measured using the same method. In all cases, the EDX and µEDX quantitative values approximately matched, proving the validity of this method.

July 23, 2014 GMT